Method for facilitating transportation of particulate on a conveyor belt in a cold environment

ABSTRACT

Coal and other particulate can be transported on a conveyor belt exposed to winter weather conditions with reduced slippage of the particulate on the belt surface by periodically treating the belt surface with from about 0.001 to about 0.005 gallons per square foot of belt surface (0.04-0.4 liters/sq. meter) of a composition containing a small amount of a dimethyl polysiloxane with the balance consisting substantially of water soluble components comprising (A) a water soluble polyhydroxy compound or monoalkyl ether thereof, and (B) a water soluble organic nonvolatile compound having at least one hydrophilic group, (A) being different from (B).

I. BACKGROUND OF THE INVENTION

A. Field of the Invention

This invention relates to a method for improving the efficiency of aconveyor belt in transporting particulate solids, particularly attemperatures below freezing, i.e., 0° C.

B. Description of the Prior Art

In transporting particulate solids such as coal, ores, gravel, and othersubstantially water insoluble particulates on conveyor belts, a seriousproblem is that in freezing temperatures, a substantial amount ofslippage occurs between the particulate and the belt surface as iceaccumulates on the belt surface, on the surfaces of the particles, or onboth. The problem is particularly severe where at least a portion of thebelt is outdoors and thus exposed to moisture from sleet and snow aswell as to moisture from condensation and that which may be on thesurface of the particulate. Obviously, such slippage results indecreased material handling efficiency, wasted energy in driving thebelt under inefficient conditions, and in severe conditions can resultin a temporary plant shut down, e.g., if coal cannot be delivered to itspoint of use at a sufficient rate to maintain a furnace or boiler atproper operating conditions.

Various techniques have been tried to alleviate the slippage problem,such as spraying the belt with ethylene glycol. Conventional antifreezecompositions, however, have not been regarded as a completely acceptablesolution to the problem, since benefits seem to be realized only at mildfreezing temperatures, e.g., temperatures above about 20° F. (-6° C).Consequently, smudge pots or heaters are often placed near a belt toheat the belt. However, in the event the conveyor must be stopped for abrief period, the heat sources near the belt are a serious hazard sincenot infrequently, the belts are burned by the heat source.

Various deicing or freeze depressant compositions have been taught,particularly for use on aircraft. Representative of this art are thefollowing patents:

Korman, U.S. Pat. No. 2,101,472, which teaches a gel containing gelatineto which is added as an antifreeze substance, glycerol and/or a glycol;West et al., U.S. Pat. No. 2,373,727, which teaches a composition suchas in Korman, but also including a hydrocarbon to provide an emulsion;Fain et al., U.S. Pat. No. 2,716,068, which teaches a composition of aglycol, at least one of potassium thiocyanate, potassium acetate, urea,or certain inorganic salts, and optionally sodium nitrite; British No.1,055,453 which teaches a deicing composition of at least one watersoluble monohydric alcohol, at least one water soluble polyhydricalcohol, and formamide or a formamide derivative; and Dawtrey et al.,U.S. Pat. No. 3,350,314, which teaches a foamable composition of water,an alkylene polyol, and a long chain aliphatic tertiary amine.

Ordelt et al., U.S. Pat. No. 3,362,910, teaches an automotive antifreezecomposition.

Scott, Jr., et al., U.S. Pat. No. 3,624,243 and 3,630,913, each relateto chemical deicers containing corrosion inhibitors making themspecially suited for use on airport runaways.

Shapiro, U.S. Pat. No. 2,454,886 relates to the prevention of mist andfrost on glass and similar sheet material.

In a commonly assigned application entitled "Method for Reducing theStrength of Ice" by Christ F. Parks and Kenneth H. Nimerick, Ser. No.855,528 filed Nov. 28, 1977, now U.S. Pat. 4,117,214 issued Sept. 26,1978 which is a continuation-in-part of Ser. No. 380,778 filed July 19,1973, now abandoned it is disclosed a multicomponent composition similarto that employed herein reduces the strength of ice, and that a mass ofparticulate solids treated with the composition may be easily brokenapart even after the mass is exposed to temperatures sufficient topermit ice to form because the ice which forms is of substantiallyreduced compressive strength.

There is no suggestion, however, that any of these formulations could beeffectively used on conveyor belts.

In an invention on which a patent application is being filedconcurrently herewith, Frank J. Beafore has discovered that thecomposition employed in the invention of Parks et al. is effective inmeeting the problem of particulate slippage on belts at temperatures ofless than 0° C. The present invention is a further refinement of theinvention of Beafore.

Finally, dimethyl polysiloxanes have been used as release agents forconveyor belts. See, for example, Dow Corning Corporation Bulletin22-082 (March, 1972) "Information About Release Agents: Dow CorningHV-490 Emulsion". However, so far as is known there has been nosuggestion to use the dimethyl polysiloxanes in the manner of thepresent invention.

II. SUMMARY OF THE INVENTION

The present invention is a method for facilitating the transportation ofparticulate solids on a conveyor belt under conditions such that atleast a portion of the belt surface is exposed to a temperature of lessthan 0° C. during operation of the belt. The crux of the invention liesin contacting the belt surface with from about 0.001 to about 0.005gallons per square foot of belt surface (0.04-0.2 liters per squaremeter) with a particular treating fluid. The treating fluid employed inthe present method contains from about 0.05 to about 2 percent by weighta dimethyl polysiloxane, with the balance consisting substantially ofwater soluble components comprising

(A) a water soluble polyhydroxy compound or monoalkyl ether thereof, and

(B) a water soluble organic nonvolatile compound having at least onehydrophilic group, compound (B) being different from (A) in any givenformulation.

The above specified rate of application is fairly critical. If toolittle is applied, an objectionable ice build-up is realized. On theother hand, too much treating fluid actually tends to lubricate the beltsurface.

By "consists substantially (or consisting substantially) of watersoluble components", is meant that compositions containing substantialquantities, i.e., about 5 percent or more, of water immiscible liquidsare not intended for use herein.

By "water soluble" in reference to each of Components (A) and (B) ismeant sufficiently soluble so that a sufficient quantity of saidcompound may be dissolved in water to noticeably affect the strength ofany ice formed from the water, when employed with the other componentsaccording to the invention. Obviously, use of Components (A) and (B)herein in quantities or proportions which would cause a significantphase separation or precipitation is generally undesirable and istherefore avoided.

Treatment of the belt with the aforementioned composition removes icealready on the belt and keeps the belt free of quantities of icedetrimental to the transportation of particulate solids on the belt forhours.

III. Further Description of the Invention

The chemical mechanism by which the present invention operates is notcompletely understood, but the ability of the composition employed toreduce the strength of ice is believed to play a significant part in itsability to keep the belt surface free from a detrimental accumulation ofice, even at fairly low concentrations and cold temperatures, e.g.,below 20° F. (-7° C.) and even below 0° F. (-18° C.). Thus, though someice may form, it is of reduced compressive strength and is easily brokenup by the moving particulate and therefore does not accumulate to anyappreciable extent. The polysiloxane is believed to help keep ice fromadhering to the belt, but alone has little if any ability to remove anyice already on the belt.

The invention may be employed with all forms of divided solids whichthemselves are neither water-soluble nor water swellable. Representativeof such materials are various forms of coal, mineral ores such asbauxite, iron ore, copper ore, taconite, and the like.

One of the ingredients (Component A) useful in the compositions employedin the present method is a water-soluble polyhydroxy compound. Apreferred group is the polyhydroxyalkanes. Typical members of that classare ethylene glycol, di-ethylene glycol, triethylene glycol, propyleneglycol, di-propylene glycol, glycerine and sugar. Of those materials, atleast a major proportion of ethylene glycol is preferred. The monoalkylethers, such as the monobutyl ether of ethylene glycol, are also useful.Mixtures of alkylene glycols may also be employed as Component A, forexample, a mixture such as ethylene glycol and 1,2-propylene glycol,preferably in an approximately 40:60 to 60:40 weight ratio to oneanother.

The second material (Component B) to be used in the treating of thefinely divided particles is a watersoluble organic nonvolatile compound.The compound is substantially nonvolatile, i.e., has a sufficiently lowvapor pressure at the conditions of use, so that substantially none ofthe compound will be lost by vaporization during use. This compoundshould have at least one hydrophilic group such as amine, carboxyl, orcarboxylate groups. The compound may be polymeric or non-polymeric.Typical of the latter are fumaric acid, urea, glycolic acid, tetrasodiumsalt of ethylene diamine tetraacetic acid, sodium acetate and aceticacid. Other amines and carboxylic materials will be known to the skilledworker. Typical of the polymeric materials are polyacrylamide(preferably but not essentially having at least 10 percent hydrolysis),polyvinyl pyrrolidone, polyethyleneimine, polyacrylates, polyamidecopolymers such as that sold commercially as Arco S-232, and the naturalgums, such as guar gum. All of the useful polymers will be of relativelylow molecular weight in order to be watersoluble. Judicious selection ofother useful polymers can be made by reference to standard referenceswith an optimum choice determined by simple preliminary experiment.

The ratio of the hydroxy compound with the organic non-volatile compoundmay be varied within wide limits, and will depend in large measure onthe particle size, the amount of moisture, the condition of exposure ofthe belt, the texture of the belt surface, the severity of incline ofthe belt path, and to some extent on the choice of chemicals employed.For example, some of the polymeric substances causes a large increase inviscosity which can make it difficult to apply using spray equipment ifused at high concentrations. As a general rule the combination ofingredients will contain about 0.001 to about 2 parts of the organicnonvolatile compound for each part of polyhydroxy compound. Optimumselection will be readily made with simple routine experiments.

Also employed in the composition employed in the present invention isfrom about 0.05 to about 0.2 percent by weight of a dimethylpolysiloxane, preferably about 0.1 to 1.5 percent. Dimethylpolysiloxanes and methods for preparing them are well known in the art.Preferably, the polysiloxane is of the type having a kinematic viscosityof at least about 100,000 centistokes. Such compounds are commonlyavailable commercially as aqueous emulsions, e.g., as Dow Corning HV-490emulsion (aqueous, 35% active polysiloxane). The addition of water tothe treating composition is generally undesirable since it dilutes thecomposition thereby at least somewhat decreasing the ability of thecomposition to act on moisture on the belt or particulate. However, solong as the total amount of water present in the treating compositionprior to use does not exceed about 5 percent by weight, the effect ofthe small amount of water added by the siloxane emulsion in negligible.

The compositions used in the treatment may also include other materialssuch as dyes, stabilizers, anti-oxidants, and other conventionally addedmaterials. However, the composition is substantially free ofcorrosioninducing metal halide salts, such as calcium chloride.

The treating composition may be applied to the belt surface in anyconvenient manner, such as with spray, brush, or roller applicators.Preferably, a spray system such as illustrated in FIG. 6 in Society ofMining Engineers Preprint 77-F-371 (October, 1977) is employed.

As hereinabove mentioned, the treating compositions are applied at arate of from about 0.001-0.005 gal/ft², and preferably about 0.002-0.004gal/ft² (0.08-0.16 l/m²). Depending on the particular compositions, andthe conditions of use, treatment, and exposure, slight variation outsidethese ranges may be tolerated, but too little treating fluid isgenerally ineffective in keeping the belt substantially free ofdetrimental ice build-up for any appreciable time, and too much fluidcan actually lubricate the belt to the extent that objectionableslippage of the particulate occurs. Similarly, the particularcompositions, and the conditions of use, treatment, and exposure willaffect the frequency of retreatment. A single treatment may be effectivefor from about 1 to as many as 8 hours or more. In general, howwever,from 1 to 4 treatments per 8-hour working shift effectively maintainstrouble free operation of the conveyor belt system.

IV. Examples

All parts and percentages are by weight, except as specifically noted.

Examples 1-3 are from said application of Parks et al. They do notspecifically illustrate use of the treatment fluids on a conveyor belt,but illustrate that blends of Components A and B are synergisticallyeffective in reducing the strength of ice.

EXAMPLE 1

Ice samples were prepared by first dissolving the desired chemicals intowater. The water solution was chilled to about 40° F. before pouringinto brass molds.

The brass molds were 2" × 2" × 2". The molds were sprayed with a moldrelease agent and placed in a 0° F. freezer for several hours prior topouring the chilled water solution into the molds. The ice remained inthe molds for at least 16 hours at 0° F. before being removed fortesting.

The compressive strength of these 2" × 2"× 2" ice cubes was determinedusing a Tinius Olsen hydraulic press. The steel jaws of the press wereprecooled by placing ice between the faces and maintaining a pressure onthe ice while it was melting. The cooling time was about five minutes.The ice cubes were then inserted between the steel plates and the platesclosed by hydraulic pressure at a rate of 1.7 centimeters per minute.The pressure at which the ice broke was recorded.

The results are shown in Table I.

                  TABLE I                                                         ______________________________________                                                                  Compressive                                         Agent                     Strength (psi)                                      ______________________________________                                        --                        364*                                                0.1% polyacrylamide M.W. 6M                                                                             287                                                  (30% hydrolyzed) (A)                                                         0.2%    "                     220                                             0.5%    "                     170                                             1.0%    "                     148                                             0.1% polyacrylamide (25% hydrolyzed)                                                                    312                                                  lightly crosslinked with methylene                                            bis acrylamide                                                               0.2%    "                     220                                             0.5%    "                     280                                             1.0%    "                     185                                             0.05% ethylene glycol (EG)                                                                              358                                                 0.1%    "                     245                                             0.25%   "                     225                                             0.5%    "                     265                                             1.0%    "                     195                                             2.5%    "                     95                                              5.0%    "                     50                                              0.05% EG + 0.1 (A)        280                                                 0.1%    "                     198                                             0.25%   "                     120                                             0.5%    "                     95                                              1.0%    "                     97                                              2.5%    "                     60                                              5.0% "  30                                                                    ______________________________________                                         *Average of 5 tests                                                      

The same trend in the reduction of strength of the ice was shown whenthe rate of jaw closure was increased to 4 centimeters per minute.

EXAMPLE 2

Numerous materials were used to demonstrate their effectiveness inreducing the strength of ice. The samples were prepared and testedaccording to the procedures of Example 1. The results are shown in TableII.

                  TABLE II                                                        ______________________________________                                                                  Compressive                                                                   Strength                                            Agent %                   (psi)                                               ______________________________________                                        --                        384                                                 2.5 Ethylene glycol (EG)  145                                                 0.5 Polyvinyl pyrrolidone (M.W. 360,000)                                                                665                                                 0.5 Polyvinyl pyrrolidone (m.W. 360,000)                                                                130                                                  + 2.5 EG                                                                     0.5 Guar gum              1050                                                0.5 Guar gum + 2.5 EG     82                                                  0.5 Polyacrylate-polyamide copolymer                                                                    360                                                  (Arco S-232)                                                                 0.5 Polyacrylate-polyamide copolymer                                                                    115                                                  (Arco S-232)                                                                  + 2.5 EG                                                                     0.5 Polyacrylamide 6M M.W. 30% hydrolysis                                                               445                                                 0.5 Polyacrylamide 6M M.W. 30% hydrolysis                                                               67                                                   + 2.5 EG                                                                     0.5 Polyacrylamide-cationic form                                                                        232                                                 0.5 Polyacrylamide-cationic form + 2.5 EG                                                               45                                                  0.5 Sodium polyacrylate   372                                                 0.5 Sodium polyacrylate + 2.5 EG                                                                        115                                                 0.5 Gelatin               525                                                 0.5 Gelatin + 2.5 EG      52                                                  0.5 (75% polyacrylamide-25% gelatin) + 2.5 EG                                                           93                                                  0.5 (50% polyacrylamide-50% gelatin) + 2.5 EG                                                           93                                                  0.5 (25% polyacrylamide-50% gelatin) + 2.5 EG                                                           50                                                  0.5 Polyacrylamide-nonionic                                                                             610                                                 0.5 Polyacrylamide-nonionic + 2.5 EG                                                                    65                                                  2.5 Urea                  750                                                 2.5 Urea + 2.5 EG         100                                                 2.5 Glycolic acid         345                                                 2.5 Glycolic acid + 2.5 EG                                                                              62                                                  2.5 Tetrasodium salt of ethylene diamine                                                                297                                                  tetraacetic acid                                                             2.5 Tetrasodium salt of ethylene diamine                                                                82                                                   tetraacetic acid + 2.5 EG                                                    2.5 Sodium acetate        220                                                 2.5 Sodium acetate + 2.5 EG                                                                             90                                                  0.1 Acetic acid           492                                                 0.1 EG                    265                                                 0.1 Acetic acid + 0.1 EG  115                                                 0.5 Acetic acid           325                                                 0.5 EG                    265                                                 0.5 Acetic acid + 0.5 EG  102                                                 2.5 Acetic acid           267                                                 2.5 EG                    95                                                  2.5 Acetic acid + 2.5 EG  50                                                  2.5 Ethylene glycol monobutyl ether                                                                     317                                                 2.5 Ethylene glycol monobutyl ether + 0.5                                                               190                                                  polyacrylamide M.W. 6M (30% hydrolysis)                                      2.5 Diethylene glycol     97                                                  2.5 Diethylene glycol + 0.5% polyacrylamide                                                             57                                                   M.W. 6M (30% hydrolysis)                                                     2.5 Sugar                 302                                                 2.5 Sugar + 0.5% polyacrylamide M.W. 6M                                                                 175                                                  (30% hydrolysis)                                                             2.5 Sodium lignate        537                                                 2.5 Sodium lignate + 0.5 polyacrylamide                                                                 490                                                  M.W. 6M (30% hydrolysis)                                                     2.5 Triethylene glycol    215                                                 2.5 Triethylene glycol + 0.5 polyacrylamide                                                             80                                                   M.W. 6M (30% hydrolysis)                                                     ______________________________________                                    

EXAMPLE 3

Additional tests using a mixture of ethylene glycol and 1,2-propyleneglycol as Component (A) were carried out as in Examples 1 and 2, exceptthat a Baldwin hydraulic press was employed at a jaw closure rate of 7.8cm/min. Results were as follows:

    ______________________________________                                        Agent, %            Compressive Strength, psi                                 ______________________________________                                        Water only          348                                                       1.25% propylene glycol + 1.25%                                                                    124                                                         ethylene glycol                                                             2.5% sodium acetate 115.5                                                     2.5% a blend of 47.5% ethylene                                                                    95                                                          glycol, 47.5% propylene glycol,                                               and 5% sodium acetate                                                       ______________________________________                                    

The foregoing blend of glycols and sodium acetate may be safely employedwith routine precautions and safety equipment, making it attractive foruse even by individuals with little training. The blend has beenaccepted for use in underground mines by the Mining Enforcement andSafety Administration of the U.S. Department of the Interior. Moreover,it is substantially non-corrosive, does not significantly affect coalprocessing steps, e.g., froth flotation, and does not leave quantitiesof residues detrimental to blast furnace or coking operations.

In the following Examples, "FCA" denotes the 47.5% ethylene glycol,47.5% propylene glycol, 5% sodium acetate treating fluid tested inExample 3.

EXAMPLE 4

A Pennsylvania coal preparation plant was experiencing icing on a refuseconveyor belt, causing abnormal slippage of the particulate along thebelt surface. The total length of the belt was about one mile. FCA wassprayed on the 36-inch wide belt at a rate of about 0.006-0.015 gallonper linear foot. At the time of application, the temperature was -15° C.(+5° F.) and winds were reported at about 25 miles per hour. Followingtreatment, the belt was immediately placed back in service, and nonoticeable product slippage or detrimental ice accumulation was observedfor several hours.

EXAMPLE 5

A butyl rubber inner tube was cut into approximately 6 inch squares. Toeach except the control was applied 0.0025 gal/ft² of a treating fluid.The corners of each square were brought together to form a cup, each cupwas filled with about 100 ml. of water and then placed in a 0° F.freezer for one day. Each cup was removed from the freezer, the ice wasimmediately removed as well as possible from the rubber, the cuprefilled with water but without another treatment, and returned to thefreezer. After two days, each cup was again cleaned, refilled, andrefrozen. A final observation was made five days later. In eachinstance, the ice was very strongly adhered to the control cup. In thecups which had initially been treated either with FCA or with the60:30:10 mixture of ethylene glycol, potassium thiocyanate, and sodiumnitrate described in Fain et al., U.S. Pat. No. 2,716,068, the ice wasnot frozen to the cup after the first two observations but was after thefinal observation. The composition of Fain et al., however, wasdifficult to prepare: some undissolved solids were present even aftertwo hours of agitation.

EXAMPLE 6

Using inner tube squares as discussed in Example 5, the effect of apolysiloxane was tested. In this test, the precise amounts of treatingfluid applied was not quantitatively measured, but visually uniformapplications were made before the cup was filled with water the firsttime. Each cycle consisted of approximately 24 hours at 0° C. Resultswere as follows:

    ______________________________________                                        Treating Fluid                                                                          Cycle 1   Cycle 2   Cycle 3 Cycle 4                                 ______________________________________                                        [None]    Stuck-Ice Not run   Not run Not run                                           will not                                                                      release                                                             FCA       Clean     Stuck     Not run Not run                                           release                                                             By volume,                                                                              Clean     Clean     Clean   Stuck                                   95% FCA   release   release   release                                         5% HV490*                                                                     HV490*    Clean     Clean     Clean   Stuck                                             release   release   release                                         ______________________________________                                         *Dow Corning HV490 emulsion, hereinabove described.                      

What is claimed is:
 1. A method for facilitating transportation ofparticulate solids on a conveyor belt, at least a portion of which isexposed to a temperature of less than 0° C., comprising:(a) contactingthe surface of said belt upon which the particulate solids aretransported with from about 0.001 to about 0.01 gallons per square footof belt surface, of a composition containing from about 0.05 to about 2%by weight a dimethyl polysiloxane, with the balance consistingsubstantially of water soluble components comprising(A) a water solublepolyhydroxy compound or monoalkyl ether thereof, and (B) a water solubleorganic nonvolatile compound having at least one hydrophilic group, saidcompound (B) being different from said compound (A), said compositionbeing substantially free of corrosion inducing metal halide salts; (b)placing particulate solids on the treated belt; (c) moving the belt sothat said solids are transported; and (d) exposing at least a portion ofthe treated belt surface to a temperature of less than 0° C.
 2. Themethod of claim 1 wherein said belt is in substantially continuousservice and said step (a) is carried out periodically, with from aboutone to about eight hours between treatments.
 3. The method of claim 1wherein the particulate solid is coal.
 4. The method of claim 1 whereinthe hydrophilic group in (B) is amine, carboxyl, or carboxylate.
 5. Themethod of claim 1 wherein the polyhydroxy compound is aliphatic.
 6. Themethod of claim 1 wherein (A) is at least one alkylene glycol.
 7. Themethod of claim 6 wherein (B) is selected from the group consisting ofpolyacrylamide, glacial acetic acid, and sodium acetate.
 8. The methodof claim 7 wherein (A) consists of ethylene glycol.
 9. The method ofclaim 8 wherein (B) consists of glacial acetic acid.
 10. The method ofclaim 6 wherein (A) consists of a mixture of ethylene glycol andpropylene glycol and (B) consists of sodium acetate.
 11. The method ofclaim 10 wherein the ethylene glycol, propylene glycol and sodiumacetate are present in a weight ratio to one another of about40-60:60-40:5.
 12. The method of claim 11 wherein the siloxane is of thetype having a viscosity of about 100,000 centistokes.
 13. The method ofclaim 11 wherein the particulate is coal having a particle size of lessthan about 2 inches.
 14. The method of claim 1 wherein the siloxane isof the type having a viscosity of about 100,000 centistokes.
 15. Themethod of claim 1 wherein the weight ratio of (B) to (A) is from about0.001:1 to about 2:1.
 16. The method of claim 1 wherein the rate ofapplication is from about 0.002-0.004 gallons per square foot.